1. Field of the Invention
This invention relates generally to compositions for adsorbing hydrocarbon molecules that have vaporized and more particularly to compositions and structures useful in hydrocarbon-fueled engines such as generators, motor vehicles and similar applications for scavenging hydrocarbon molecules from raw fuel that may be present in one or more systems of the engine including but not limited to the air intake system.
2. Description of Related Art
As automotive emission requirements have become much more stringent, the emission of hydrocarbons from sources other than the fuel tank and the exhaust of motor vehicles is subject to increasing federal regulation. Significant levels of hydrocarbon emission may come from such diverse sources as vehicle tires, seats and other interior and exterior components. However, a major source of hydrocarbon emission is the raw fuel that remains in the engine air/fuel intake system of the motor vehicle after the engine is shut off.
Accordingly, this invention is particularly concerned with the adsorption or scavenging of hydrocarbon molecules emitted from raw fuel in the air intake system of a vehicle. When the vehicle engine is operating fuel is consumed through combustion and hydrocarbon emissions from the intake system are very low or non-existent. When the vehicle engine is turned off, raw fuel may remain within the intake manifold runners, fuel injectors, cylinders having an open intake valve, and at times in a crankcase ventilated under a positive pressure. This raw fuel, unless dealt with, will evaporate after the vehicle engine is turned off and can be a significant source of undesirable hydrocarbon emission. A major portion of the raw fuel evaporates through the air intake system of the engine.
In the past, carbon particles, especially activated carbon and zeolites have been used to scavenge or adsorb hydrocarbon molecules. These scavengers have typically been used in a bulk form, or as bags of loose particles. Occasionally bags or loose particles of a hydrocarbon scavenger, such as activated carbon are found within fiber or ceramic like structures. While bags of loose carbon particles adsorbed hydrocarbons relatively efficiently, they are not easily adapted to adsorbing hydrocarbons from the intake systems of motor vehicles. Moreover, these prior arrangements while being effective to scavenge hydrocarbons from the immediate environment, they are not set up to give up or deliver the adsorbed hydrocarbon in any meaningful or efficient manner.
Activated carbon particles bound within fiber or ceramic like structures provide a more usable physical form but the adsorption characteristics of such structures are poor because large portions of the carbon surface are masked or bound to the supporting structure thus limiting the capacity of the structure to adsorbed hydrocarbons. Also, fiber or ceramic-based adsorbing elements generally have a low effective surface area so there is an undesirably high surface area to air flow ratio. These elements also are usually substantially rigid and this increases the difficulty of incorporating them into engines and particularly into the air intake system of a motor vehicle engine.